A little something about global warming.

Global warming is the increase in the average measured temperature of the Earth's near-surface air and oceans since the mid-twentieth century, and its projected continuation. Some of the causes are deforestation, melting ice caps, greenhouse effect, the use of chlorofluorocarbon (CFC) and the thinning of the ozone layer. In result, the temperature of the earth increases. The term "global warming" refers to the warming in recent decades and its projected continuation, and implies a human influence.

The Earth's climate changes in response to external forcing, including variations in its orbit around the Sun (orbital forcing), changes in solar luminosity, volcanic eruptions, and atmospheric greenhouse gas concentrations. The detailed causes of the recent warming remain an active field of research, but the scientific consensus is that the increase in atmospheric greenhouse gases due to human activity caused most of the warming observed since the start of the industrial era.
This attribution is clearest for the most recent 50 years, for which the most detailed data are available. Some other hypotheses departing from the consensus view have been suggested to explain most of the temperature increase. One such hypothesis proposes that warming may be the result of variations in solar activity.

Sources :
http://www.dailygalaxy.com/my_weblog/global_warming/
http://en.wikipedia.org/wiki/Global_warming